Melanoma is a type of skin cancer referred to as malignant melanoma. There are various types of skin cancer. Melanoma is the type of skin cancer that has the highest grade of malignancy and thus is very dreaded. Among cells composing skin, melanin-pigment-producing cells are referred to as pigment cells (melanocytes). These cells become cancerous, and melanoma is developed.
The frequency of the occurrence of melanoma in Japan is approximately 1.5 to 2 people per population of 100,000. It is inferred that melanoma annually occurs among approximately 1,500 to 2,000 people in Japan. In the Europe and the United States, the frequency of melanoma incidence is said to be over a dozen people per population of 100,000. The frequency of melanoma incidence in Australia is 20 or more people per population of 100,000, which is said to be the highest in the world. Accordingly, people in Europe, the United States and Australia are interested in melanoma and pay attention to its occurrence. Surprisingly, it has been confirmed that the frequency of the occurrence of melanoma is increasing yearly in both Japan and countries other than Japan. In the latest survey, the annual number of fatalities due to this disease in Japan was as high as around 450 people. Melanoma afflicts people regardless of age. Melanoma occurs more frequently particularly among people aged 40 and up, and occurs most frequently among people aged 60 to 70 and up. Melanoma occurs infrequently among children, but this does not mean that no melanoma occurs among children. Currently, melanoma tends to occur more frequently among young people aged 20 to 30 and up. There are no particular tendencies for melanoma to occur more frequently either in males or females. Melanoma occurs in both males and females. Melanomas in Japanese people are most frequently developed on the soles of the feet (planta pedis). Such melanoma cases account for approximately 30% of all melanoma cases in Japan. Melanomas in Japanese people are characterized in that they are often developed in the toenails and fingernails. Furthermore, similar to melanomas in Western people, melanomas in Japanese people are developed at all skin locations, such as in the trunk, hands, feet, face, head, and the like.
Measurement of serum tumor marker is important not only in melanoma diagnosis, but also in early detection of recurrence in postoperative cases and in determination of therapeutic effects in cases at progressive stages. As tumor markers for melanoma, the usefulness of serum LDH and of 5-S-cysteinyldopa (5-S-CD) has been known to date. In more recent years, S-100β protein and melanoma inhibitory activity (MIA) protein have been reported as more sensitive markers. In Japan, 5-S-CD is broadly used as a tumor marker for melanoma. However, none of these tumor markers yield positive results unless the melanoma is at a highly advanced stage, such as Stage IV. Therefore, it must be said that the usefulness of these tumor markers is limited in terms of melanoma diagnosis and early detection of postoperative recurrence.
The present inventors have previously reported that the glypican-3 (GPC3) is a secretory protein, that GPC3 can be detected in the serum of 40% of hepatocellular carcinoma patients and 40% of melanoma patients using the ELISA method, and that GPC3 is useful as a novel tumor marker for hepatocellular carcinoma (Nakatsura T. et al., Biochem. Biophys. Res. Commun. 306, 16-25 (2003); and Nakatsura, T. et al., Clin. Cancer Res. 10, 6612-6621, 2004).
SPARC (Secreted protein, acidic rich in cysteine, also known as osteonectin or BM-40) was reported in 1981 by Termine et al., as a protein constituting bone. SPARC was also reported in 1987 by Mann et al., as a constituent of the stroma of neoplasm of a basal membrane (Termine J D et al., Cell, 26: 99-105, 981; and Mann K et al., FASEB J 218: 167-172, 1987).
SPARC is an intercellular cement glycoprotein having various functions. The major functions of SPARC include inhibition of cell adhesion, inhibition of cell proliferation, and regulation of intercellular cement, for example (Bradshaw and Sage, J. Clin. Invest, 107: 1049-1054, 2001; and Brekken and Sage, Matrix Biol., 2001; 19: 816-827). SPARC regulates interaction between intercellular cement and cells through binding of structural proteins of such intercellular cements such as collagen.
In a human adult, SPARC is expressed at high levels in bone, blood platelets, wounded sites, or sites such as tumor sites where tissues are repeatedly reconstructed. There are many reports concerning the relationship between SPARC and tumors concerning various types of carcinoma. Tumor cells or host interstitial cells and inflammatory cells in tumor tissues express SPARC.
Ledda et al. have reported that SPARC expression in human melanoma correlates with tumor progress as determined by immunohistological tests (Ledda et al., J. Invest. Delmatol., 108, 210-214, 1997). Furthermore, Ledda et al. have reported that suppression of SPARC expression in human melanoma cells using a SPARC antisense expression vector results in in vitro disappearance of adhesion properties and infiltration properties and in vivo disappearance of carcinogenicity (Ledda et al., Nature Med., 3, 171-176, 1997).